Settler: history releases settle after half an hour

A release whose last post is 6 hours old gets nothing from the tail, only
fragments from neighbouring ranges: settled once unchanged for 30 minutes.
Waiting 6 hours after it was read held every history release back from
phase 2 after each reset; with the hourly sweeps' resets the prober (and so
the par2 merge) never had work.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/functional/settler.spec.ts

@@ -16,4 +16,16 @@ test.group('Settler', (group) => {
     const byName = Object.fromEntries((await db.from('releases').select('name', 'complete', 'settled_at')).map((r) => [r.name, [r.complete, r.settled_at !== null]]))
     assert.deepEqual(byName, { a: [true, true], b: [false, true], c: [null, true], d: [null, false] })
   })
+
+  test('settles history releases (posted long ago) once unchanged for half an hour', async ({ assert }) => {
+    const posted = new Date('2015-01-01T00:00:00Z')
+    const row = (key: string, lastSeen: Date, lastPosted: Date) => ({
+      release_key: key.padEnd(40, '0'), identity_key: key.padEnd(40, '0'), name: key, source: 'subject', groups: '[]', files: 1, last_seen_at: lastSeen, posted_at: lastPosted, last_posted_at: lastPosted,
+    })
+    const minutesAgo = (m: number) => new Date(Date.now() - m * 60_000)
+    await db.table('releases').multiInsert([row('old', minutesAgo(31), posted), row('fresh', minutesAgo(5), posted), row('tail', minutesAgo(31), minutesAgo(40))])
+    assert.equal(await Settler.run(), 1)
+    const settled = (await db.from('releases').whereNotNull('settled_at').select('name')).map((r) => r.name)
+    assert.deepEqual(settled, ['old'])
+  })
 })